Previous studies have shown that resting left ventricular dimensions and basal ejection fraction are useful indices of cardiac function for the assessment and follow-up of patients with aortic regurgitation. However, the relation to the inotropic reserve of the myocardium has not been investigated previously. To address this issue, we studied the response of increasing doses of dobutamine (2.5 to 20 microg/kg/min) during transesophageal examination in 14 patients with aortic regurgitation who were asymptomatic and had normal resting ejection fraction. In each of these patients, there was dilatation of the left ventricle as a consequence of the valvular disorder. The myocardial inotropic reserve was measured as systolic thickening at each dose of dobutamine. In the overall group of patients studied, no correlation was observed between the myocardial response to dobutamine and resting left ventricular dimensions or ejection fraction. Thus, the results of this study indicate that the myocardial inotropic reserve in patients with aortic regurgitation is not related to either the degree of dilatation or the systolic function at rest of the left ventricle. It remains to be determined whether this index of myocardial contractile state is a predictor of further left ventricular dilatation, dysfunction, or development of symptoms during follow-up that may indicate need for aortic valve replacement.